Nenad Đ. Zrnić

Mathematical Models of Multiserver Queuing System for Dynamic Performance Evaluation in Port

We discuss dynamic system performance evaluation in the river port utilizing queuing models with batch arrivals. The general models of the system are developed. This system is modelled by queue with finite waiting areas and identical and independent cargo-handling capacities. The models are considered with whole and part batch acceptance (or whole and part batch rejections) and the interarrival and service times are exponentially distributed. Results related to the batch blocking probability and the blocking probability of an arbitrary vessel in nonstationary and stationary states have been obtained. Numerical results and computational experiments are reported to evaluate the efficiency of the models for the real system.

Appropriate Modeling of Dynamic Behavior of Quayside Container Cranes Boom Under a Moving Trolley

The paper deals with the analysis of moving trolley effects on the dynamic behavior of flexible structure of a mega high-performance quayside container crane (QCC) boom. The boom is modeled as a system with distributed parameters, comprising reduced stiffnesses and lumped masses from other parts of the upper structure. This paper looks both at the “moving force” and “moving mass” trolley modeling approaches to achieve the required performance of the QCC boom structure. Deterministic simulation for both considered approaches gives dynamic structural response of the boom for container transfer from quay-to-ship. The obtained results for “moving force” and “moving mass” models are compared in the scope of real values of parameters and future expectations in design of QCC. The conclusions lead to an appropriate way of model selection that can be used by engineers in practice.

External Load Variability of Multibucket Machines for Mechanization

This paper discusses the problems of identifying external loads of multibucket machines for mechanization. External loads are dominantly dynamic with distinguished stochasticity in certain cases. The paper presents the procedures for determining external loads caused by resistance-to-excavation (for bucket wheel excavators) or grabbing soil (for bridge-type coal stacker-reclaimers), as well as a short description of the model upon which is based and defined the response of the stacker-reclaimer to the external changeable load. It points to the significance of the problem of identifying the external load, as well as to the potentially very detrimental and dangerous consequences of eventual shortcomings during solving the mentioned problem.

Dynamic Responses of Mobile Elevating Work Platform and Mega Container Crane Structures

The modern design methods lead to the objectivisation of the process of thinking, which is important for the new system development. The aim of objectivisation and decomposition of the design is obvious: it should enable a new approach in the problem solving and thinking of the designer, enriches the large quantity of new information, facts and ideas, which are important for the system designing. The first part of this paper gives a brief presentation of mobile elevating work platform structure response to the wind excitation in possible resonant states. The second part is dedicated to the dynamic analysis of the mega container crane structure subjected to the moving load.

Redesign of the Bucket Wheel Excavators Substructures Based on the Comparative Stress – Strain Analysis

Failures caused by heavy duty conditions, as well as the changes of technological requirements, are basic reasons for the redesign of specific substructures of the bucket wheel excavators (BWE). The efficient redesign should be based on subtle external load identification and sufficient accuracy of stress – strain states determination. This paper gives solutions of reconstruction and comparative stress analyses for original and redesigned representative and vital BWE subsystems - slewing platform, undercarriage and two wheel bogie. The efficiency of these reconstructions is unquestionably confirmed by failureless service of mentioned subsystems.